Rabbit pulmonary angiotensin-converting enzyme has been solubilized and isolated in this laboratory as a pure water-soluble glycoprotein containing one molar equivalent of tightly bound zinc. 1. Antibody produced by goats will be examined with respect to anticatalytic activity both in vitro and in vivo. Immunologic homology with converting enzymes from other species will be investigated using anti-rabbit enzyme antibody as a probe. Classical immunodiffusion methods and assays for cross-anticatalytic activity will be employed. 2. The effect of replacing zinc with other heavy metals on catalytic parameters of the pure enzyme will be determined. 3. The catalytic and immunologic properties of the pure enzyme will be compared with those of isolated membranes containing it to establish whether participation in membrane structure alters kinetic parameters or substrate specificity (allotopy). BIBLIOGRAPHIC REFERENCES: Soffer, R.L. (1976) Angiotensin-Converting Enzyme and the Regulation of Vasoactive Peptides. Ann. Rev. Biochem. 45, in press. Soffer, R.L., Das, M., Caldwell, P.R.B., Seegal, B.C. and Hsu, K.C. (1976) Biology and Biochemistry of Angiotensin-Converting Enzyme. Agents Actions 6, in press.